Interaction between Y-Al-Si-O glass-ceramics for environmental barrier coating materials and Ca-Mg-Al-Si-O melts

Y₂O₃-Al₂O₃-SiO₂ (Y-Al-Si-O, YAS) glass is a highly promising material offering resistance against calcium magnesium aluminosilicate (Ca-Mg-Al-Si-O, CMAS) corrosion, and it is an excellent candidate for environmental barrier coating (EBC). In this study, influence of composition on YAS glass properties and CMAS corrosion resistance at 1300 °C was investigated, and the result indicated that most sets of YAS glass possessed the superior CMAS resistance than yttrium disilicate. The increase of Y₂O₃ content and decrease of Al/Si ratio both resulted in a higher nucleation rate during heating. Moreover, when YAS was subjected to the molten CMAS corrosion, two types of corrosion restraining behaviors were observed. One is the generation of anorthite layer on YAS with high-optical basicity, and the recession depth becomes less than that of yttrium disilicate. Stacking of anorthite grains obstructs the diffusion of Y to the corrosion front, which inhibits the corrosion. The other mechanism involves the generation of calcium yttrium cyclosilicate layer at ~1270 °C first on YAS with low-optical basicity. Next, with the increase in the temperature, the reaction changes to generate an amorphous phase. Moreover, the layer acts as a barrier to restrain the corrosion. Furthermore, the difference between the two corrosion behaviors was explained based on the optical basicity (OB) theory calculation, and a YAS composition region with excellent resistance toward CMAS corrosion was predicted. The region with an OB higher than that of CMAS shows superior CMAS resistance, in particular, for the portion with a lower difference in values of OB between the two substances.